Small combustion engines can be used in a wide variety of power equipment. For instance, a pressure washer, log splitter, lawnmower, air compressor, generator or the like can use an internal combustion engine to power a working component (e.g., a high pressure water pump, hydraulic pump, cutting blade). In typical pressure washers, a speed regulation system can be provided for maintaining the engine speed within a governed speed range. Referring to FIG. 1, a typical speed regulation system can include a pivoting or fixed governor arm 110 that is rotationally coupled to a rotatable shaft of a centrifugal or air vane/foil governor device coupled to an engine. Pivoting or fixed governor arm 110 can connect the centrifugal device to a throttle control TC of the engine. Specifically, a governor rod 112 can connect pivoting governor arm 110 to throttle control TC. In addition, a governor rod spring 114 can be provided to dampen fluctuations in the position of governor arm 110 caused by small variations in the engine speed. Governor arm 110 can further be connected to a fixed frame element 120 by a governor spring 116 for helping to return governor arm 110 to its initial position once the engine speed is reduced.
In this common configuration, as the speed of the engine increases, a moment is generated on the rotatable shaft of the centrifugal device, which in turn causes the rotation of governor arm 110. This rotation moves governor rod 112 to move throttle control TC toward a closed position. In this way, the speed regulation system maintains the engine speed within a predefined governed speed range.
The particular governed speed range can be set by adjusting the tension on governor spring 116. For instance, this adjustment can typically involve bending the portion of governor arm 110 that is connected to governor spring 116 or changing the spring mount on frame element 120. This adjustment is usually only made at the time of manufacture or while the engine is being serviced. As a result, in order to achieve the best possible performance, equipment manufacturers tend to set the governed speed range to a relatively high engine speed to maximize the pump flow, pressure, cutting performance, or other performance characteristic. Because the governor speed range is not easily adjustable, the engine runs in this high speed range regardless of whether or not the pump or blade is doing work.
With regard to pumps in particular, this single governed speed range can be problematic due to the fact that pumps generally exhibit two basic engine load scenarios. In a first mode, a valve is actuated to allow the pump to pressurize and flow fluid and do work. In this condition, the pump is applying a very high load to the engine. In a second mode, the valve is not actuated, which does not allow the pump to flow water or do any net work. In this condition, the pump is applying a very light load to the engine. As a result, typical use involves a significant amount of time where the valve is not being actuated and the pump is not doing work. Accordingly, there are several problems that exist because the engine runs at a high speed even in its unloaded state (i.e., when the valve is not being actuated), including high levels of noise emitted from the engine, reductions in pump life and engine life by running at a high speed, and higher fuel consumption than it would be at a lower speed.
Accordingly, it would be advantageous for a small power machine such as a pressure washer, log splitter, lawnmower, air compressor, generator or the like to include a control system that can achieve a large automatic reduction in engine idling speed without requiring any additional system integration, such as a water pressure control line tied into the pressure washer pump. At the same time, it is further advantageous that the engine still responds quickly (i.e., resumes high speed operation) when a load is applied.